In a transmission network composed of wavelength division equipments, for the wavelength service scheduling, there is certain constraint characteristic in a physical link layer and a wavelength channel layer, and there is certain constraint characteristic in multiple physical transmission links in each node in terms of service scheduling. Not all physical transmission links in each node can implement service scheduling between each other.
Wavelength service scheduling is basically up-and-down or straight-through in each node, without the capability of wavelength conversion, and this is true of a reconfigurable optical add-drop multiplexer (ROADM) system composed of a wavelength blocker (WB) and a wavelength selective switch (WSS). For a DWDM (dense wavelength division multiplexing) wavelength division equipment in which a sub-transparent multiplexing (TMUX) and the ROADM apply, due to the limitation of physical hardware conditions, the cross capability design of the TMUX is often insufficient for the crossover capability, and the wavelength channels among links in the nodes can't realize all-optical wavelength cross. When either the DWDM wavelength division equipment, or a synchronous digital hierarchy (SDH), or a synchronous optical network (SONET) or an optical transport network (OTN) is applied in a multi-level blocking cross network model for network equipment, the existing standards can't support this application sufficiently.
The switchable constraint characteristic between links only illustrates whether there is the possibility of switching between links. If service scheduling is possible on the link layer, whether service scheduling can be realized or not should also depend on the constraint characteristic of the layer of wavelength channel in the link. Service scheduling capability should be analyzed from constraint characteristics of two layers:
1. the switchable constraint capability between links in a node
in a DWDM equipment network realized by multidimensional ROADM technology, generally, if it's possible to implement service scheduling on the link layer between links of two directions in a node, the links of two directions are connected to each other by optical fibers inside. If the links of two directions are not connected to each other by optical fibers, there is no service scheduling capability between the two links. Every set of links of two directions in a system comprise a group and the service scheduling capability of each group is represented by bit. 1 means the two links in a group have the service scheduling capability between them on the physical link layer, while 0 means the two links in a group don't have the service scheduling capability between them on the physical link layer. Take an 8-dimensional ROADM as an example. Every set of links of two directions in the system comprise a group and there are a total of 7×8/2=28 groups in the system. The fixed combinations show that it's possible that transport links of two specific directions have the service scheduling capability between them on the link layer. The following Table 1 shows such combinations.
TABLE 1Corresponding relationship between link groups and bits in a nodeABCDEFGHA1234567B8910111213C1415161718D19202122E232425F2627G28H
2. the scheduling capability between wavelengths in each link in a node
in the blocking cross network model as shown in FIG. 1, wherein a switching unit DXC (digital cross connect equipment) implements electrical cross or optical cross. A west terminal equipment (TE) link distributes wavelengths in the link into different switching units through a DWDM wavelength division equipment, which is also true of the east TE link. Wavelength switching can be achieved only when the wavelength in the west TE link and that in the east TE link are in one switching unit. In the DWDM equipment realized by the conventional ROADM technology, wavelengths are basically up-and-down or straight-through in each node and wavelength switching is impossible. Such a collection which limits wavelength switching in the link is defined as a wavelength switching group (or wavelength group). The wavelength collection in each link which is in one wavelength switching group (or wavelength group) can realize wavelength conversion, while wavelengths in each link which are not in one wavelength group can't realize wavelength conversion. For link wavelengths only with the capability of up-and-down or straight-through, the same wavelength is a wavelength switching group (or wavelength group).
However, in the existing technology, in a blocking cross network, only the available link bandwidth information is considered as the general condition for routing calculation. In such way, in the process of call connection establishment control, selection of service path and wavelength will be tried again and again, which brings the complicated signaling control process, making the time which is used in service establishment and recovery uncertain.